Optical measurement device

ABSTRACT

A white light confocal optical measurement device capable of detecting abnormalities in a received light waveform; the optical measurement device includes: a light source; an optical system; a light receiving unit; and a processor configured to compute the distance from the optical system to the measurement object on the basis of a received light intensity of the wavelength components received in the light receiving unit. The processor compares a received light intensity of a wavelength component to a reference value for the wavelength component for a plurality of wavelength components in a waveform representing the light received, and detects an abnormality in the received light waveform when the amount of change in the received light intensity compared to the reference value therefor is greater than or equal to a predetermined threshold for any wavelength component in the plurality of wavelength components.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/413,866 filed Jan. 24, 2017 which is incorporated in its entirety byreference herein and which claimed the benefit of priority under 35U.S.C. § 119(b) to Japanese Pat. Appl. No. 2016-060274 filed on Mar. 24,2016.

BACKGROUND Field

The present description relates to a measurement device capable ofmeasuring, for example, the surface topography of a measurement objectusing white light confocal measurement principles.

Description of the Related Art

White light confocal optical measurement devices are known as devicesused for examining the surface topography of a measurement object. Thiskind of optical measurement device includes a light source generatingillumination light including a plurality of wavelength components, anoptical system configured to introduce an axial chromatic aberrationinto the illumination light from the light source, a light receivingunit configured to separate the reflection light received from anoptical system into wavelength components and to receive the lighthaving the wavelength components, and a light guide optically connectingthe light source, the optical system, and the light receiving unit. Forinstance, Japanese Patent Application Publication No. 2012-208102discloses a confocal measurement device that uses confocal optics forcontactless measurement of the displacement of a measurement object.

SUMMARY

An optical measurement device according to one aspect of the inventionincludes a light source configured to emit illumination light includinga plurality of wavelength components; an optical system configured tointroduce an axial chromatic aberration into the illumination light fromthe light source and to receive reflection light reflecting from ameasurement object where at least a portion of the measurement objectlies along a line extending from the optical axis of the optical system;a light receiving unit configured to separate the reflection lightreceived at the optical system into wavelength components and therebyreceive the light having the wavelength components; and a processorconfigured to compute the distance from the optical system to themeasurement object on the basis of a received light intensity of thewavelength components received in the light receiving unit. Theprocessor compares a received light intensity of a wavelength componentto a reference value for the wavelength component for a plurality ofwavelength components in a waveform representing the light received, anddetects an abnormality in the received light waveform when the amount ofchange in the received light intensity compared to the reference valuetherefor is greater than or equal to a predetermined threshold for anywavelength component in the plurality of wavelength components.

The above-mentioned configuration provides a white light confocaloptical measurement device capable of detecting abnormalities in areceived light waveform. Note that “the distance from the optical systemto the measurement object” is the distance from the optical system to ameasurement position on the measurement object, and is not necessarilythe shortest distance from the optical system to the measurement object.The “measurement position” is the position on the measurement objectirradiated by the illumination light from the light source. Themeasurement position is not limited to being one position on themeasurement object.

The processor may measure the displacement of the measurement object onthe basis of a peak wavelength in the received light waveform when theamount of change in the received light intensity is less than thethreshold for at least one of the plurality of wavelength components.

The above-mentioned configuration is capable of detecting an abnormalwaveform on the basis of the received light intensity in anotherwavelength even if one of the wavelengths selected from among theplurality of wavelengths coincides with the measurement wavelength.

The plurality of wavelength components may include five wavelengths. Theabove-mentioned configuration is capable of detecting an abnormalwaveform on the basis of the received light intensity within a singlewavelength even when four of the wavelengths selected from among thefive wavelengths coincides with the measurement wavelengths and theobject to be measured is configured from two transparent bodies (such asglass) with a spacer therebetween.

The threshold may be defined for each wavelength on the basis of thespectrum emitted by the light source. The above-mentioned configurationis capable of more precise detection of an abnormal waveform byestablishing a threshold for each wavelength.

An optical measurement device according to another aspect of theinvention includes a light source configured to emit illumination lightincluding a plurality of wavelength components; an optical systemconfigured to introduce an axial chromatic aberration into theillumination light from the light source and to receive reflection lightreflecting from a measurement object where at least a portion of themeasurement object lies along a line extending from the optical axis ofthe optical system; a light receiving unit configured to separate thereflection light received at the optical system into wavelengthcomponents and thereby receive the light having the wavelengthcomponents; and a processor configured to compute the distance from theoptical system to the measurement object on the basis of a receivedlight intensity of the wavelength components received in the lightreceiving unit. The processor compares a reference value for a receivedlight intensity and the received light intensity of a wavelengthcomponent outside a wavelength domain equivalent to a measurement rangeused to measure the displacement of the measurement object, and detectsan abnormality in the received light waveform representing the receivedlight intensity when the amount of change in the received lightintensity compared to the reference value therefor is greater than orequal to a predetermined threshold.

The above-mentioned configuration is capable of monitoring the receivedlight waveform while reducing the effects to measuring the displacementof the object.

The optical measurement device according to any of the above-mentionedaspects of the invention may be configured so that the processorprovides a notification when an abnormality is detected.

The above-mentioned configuration makes the user aware that the receivedlight waveform from the optical measurement device is abnormal. Hereby,the user may take the appropriate steps to remove the cause of theabnormality. Accordingly, this allows the optical measurement device tocontinue to perform highly accurate displacement measurements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for explaining the principles of measuringdisplacement through white light confocal measurement;

FIGS. 2A and 2B are schematic views for describing the configuration ofthe light guide in an optical measurement device according to theembodiments;

FIG. 3 is a schematic view depicting an example device configuration ofan optical measurement device according to an embodiment;

FIG. 4 is a schematic view for explaining the reflection of a portion ofthe illumination light partway through the light guide;

FIG. 5 is a schematic view for explaining the problems that arise when aportion of the illumination light is reflected partway through the lightguide;

FIGS. 6A and 6B are for describing how received signals are processedwithin an optical measurement device according to the embodiment;

FIG. 7 is a schematic waveform diagram for explaining how the opticalmeasurement device assesses abnormalities according to the firstembodiment;

FIG. 8 is a diagram for explaining how the optical measurement deviceaccording to the embodiment measures the displacements of a plurality ofsurfaces on the measurement object;

FIG. 9 schematically illustrates changes in the received light intensityof background components when a portion of the illumination lightreflects partway through the light guide;

FIG. 10 illustrates an example of the relationship between a monitoredwavelength and a threshold;

FIG. 11 is a flowchart for explaining the process of detecting anabnormal waveform according to the first embodiment;

FIG. 12 is a diagram for describing the spectrum emitted by the lightsource to explain the process of detecting an abnormal waveformaccording to the second embodiment; and

FIG. 13 is a flowchart for explaining the process of detecting anabnormal waveform according to the second embodiment.

DETAILED DESCRIPTION

Technical Problem

For displacement sensors that use white light confocal principles,changes such as increases in returning light, tend to affectmeasurement. At present, it is not possible to detect these kinds ofchanges in the received light waveform, and the user is not aware thatthe received light waveform is abnormal. The user may continue to usethe sensor, unaware of the increase in returning light, and unaware thatthe increase is reducing the measurement accuracy of the sensor.

Embodiments of the present invention provide a white light confocaloptical measurement device capable of detecting abnormalities in areceived light waveform.

Effects

Embodiments of the present invention can detect abnormalities in areceived light waveform in a white light confocal optical measurementdevice.

Embodiments of the present invention are described in detail withreference to the drawings. The same or corresponding elements within thedrawings are given the same reference numerals and the explanationstherefor are not repeated.

A. Further Background and Overall Configuration

First, the problems to be addressed by an optical measurement deviceaccording to embodiments of the invention and an overview of aconfiguration for solving these problems are described.

FIG. 1 is a diagram for explaining the principles of measuringdisplacement through white light confocal measurement. Referring to FIG.1 , the optical measurement device 1 includes a light source 10, a lightguide 20, a sensor head 30, a light receiving unit 40, and a processor50. The sensor head 30 contains a chromatic aberration unit 32 and anobjective 34; the light receiving unit 40 includes a spectrometer 42 anda detector 44.

The illumination light, which contains various specific wavelengthsgenerated by the light source 10, propagates through the light guide 20and arrives at the sensor head 30. The light radiating from the lightsource 10 is focused by the objective 34 in the sensor head 30 andilluminates the measurement object 2. As the illumination light passesthrough the chromatic aberration unit 32, the chromatic aberration unit32 generates an axial chromatic aberration therein; therefore, theillumination light emerging from the objective 34 has focal points thatdiffer by wavelength. Only light of a wavelength whose focal pointcoincides with the object 2 re-enters the confocal optical fiber in thelight guide 20 of the sensor head 30. For the sake of brevity, theexpression “reflecting only a specific optical wavelength” refers to thereflection of light with a wavelength whose focal point coincides withthe position of the object 2.

The reflection light re-entering the sensor head 30 propagates throughthe light guide 20 and enters the light receiving unit 40. In the lightreceiving unit 40, the spectrometer 42 separates the reflection lightentering therein into different wavelength components, and the detector44 detects the (radiant) intensity of each of the wavelength components.The processor 50 then calculates the distance (displacement) from thesensor head 2 to the object 44 on the basis of the detection resultsfrom the detector 30.

In the example illustrated in FIG. 1 , for instance, illumination lightcontaining a plurality of wavelengths λ1, λ2, λ3 is separated bywavelength, with an image being formed at different positions (e.g., thefirst focal point 1, second focal point 2, and third focal point 3)along an optical axis AX. The surface of the object 2 coincides with thesecond focal point 2 on the optical axis AX and so only the componentwavelength λ2 in the illumination light is reflected. The componentwavelength λ2 is detected in the light receiving unit 40, and thedistance from the sensor head 30 to the object 2 computed as equivalentto the focal position of the wavelength λ2.

The detector 44 in the light receiving unit 40 is made up of a pluralityof light receiving elements; on receiving the reflection light a lightreceiving element changes relative to the sensor head in accordance withthe shape of the surface of the object 2; consequently, the detectionresults (pixel information) from the plurality of light receivingelements in the detector 44 can be used to measure the changes indistance to (displacement of) the object 2. The optical measurementdevice 1 thereby measures the surface topography of the measurementobject 2. Note that the distance from the sensor head 30 to themeasurement object 2 is in distance from the sensor head 30 to ameasurement object position on the measurement object 2, and is notlimited to the shortest distance from the sensor head 30 to themeasurement object 2. The measurement object position is a position onthe measurement object 2 irradiated by illumination light from the lightsource 10. The measurement position is not limited to being one positionon the measurement object. For instance, two different measurementobject positions may be selected from along the direction of the opticalaxis of the sensor head 30. The distance is calculated from the sensorhead 30 to each of the measurement object positions; the differencebetween the two distances is also computed. Hereby, the thickness of themeasurement object 2 can be computed.

FIGS. 2A and 2B are schematic views for describing the configuration ofthe light guide in an optical measurement device according to theembodiments. As illustrated in FIG. 2A, the optical measurement device 1includes an input cable 21 optically coupled to the light source 10, anoutput cable 22 optically coupled to the light receiving unit 40, and asensor head cable 24 optically coupled to the sensor head 30; the inputcable 21, output cable 22, and sensor head cable 24 serve as the lightguide 20. The ends of the input cable 21 and the output cable 22 areoptically coupled through a combiner/divider type coupler 23. Thecoupler 23 is 2×1 star coupler (with two inputs to one output or oneinput to two outputs) which is equivalent to a Y-splitter; in additionto transmitting the light entering from the input cable 21 to the sensorhead cable 24, the coupler 23 splits the light entering from the sensorhead cable 24 and transmits the light to the input cable 21 and theoutput cable 22.

The input cable 21, output cable 22, and sensor head cable 24 are alloptical fibers containing a single core 202; in cross section, the core202 is sheathed in a cladding 204, a coating 206, and an exterior jacket208 in that order outwards. As illustrated in FIG. 2B, the opticalfibers in the light guide 20 of the optical measurement device 1according to the embodiment includes a plurality of cores.

B. Device Structure

FIG. 3 is a schematic view an example device configuration an opticalmeasurement device according to an embodiment. Referring to FIG. 3 , theoptical measurement device 1 according to the embodiment includes alight source 10, a light guide 20, a sensor head 30, a light receivingunit 40, and a processor 50.

The light source 10 emits illumination light containing a plurality ofoptical wavelength components, and is typically implemented using awhite-light light emitting diode (LED). Any desired kind of light sourcemay be used, so long as the light source is capable of radiating lightpossessing a range of wavelengths where the displacement width of allthe focal positions generated through the axial chromatic aberrationcovers the required measurement range.

The sensor head 30 contains a chromatic aberration unit 32 and theobjective 34; the sensor head 30 is equivalent to an optical system thatinduces an axial chromatic aberration in light radiating from the lightsource 10 and receives light reflecting from the measurement object 2with at least a portion of the measurement object 2 arranged on a lineextending from the optical axis.

The light receiving unit 40 includes a spectrometer 42, and a detector44; the spectrometer 42 separates the light reflecting from the objectand received at the optical system, i.e., the sensor head 30 into eachwavelength component; the detector 44 includes a plurality of lightreceiving elements arranged corresponding to the dispersion directionfrom the spectrometer 42. The spectrometer 42 is typically a diffractiongrating, however any desired device may be adopted therefor. Thedetector 44 may be a line sensor (one-dimensional sensor) with aplurality of light receiving elements arranged one-dimensionally tocorrespond with the dispersion direction from the spectrometer 42. Thedetector 44 may also be an image sensor (two-dimensional sensor) wherethe light receiving elements are arranged two dimensionally on thedetection surface.

In addition to the spectrometer 42 and the detector 44, the lightreceiving unit 40 includes a collimating lens 41 that collimates thereflection light emitted from the output cable 22, and a read circuit 45for outputting the results from the detector 44 to the processor 50.Furthermore, reduction optics 43 may also be provided as needed, tomodify the spot size of the reflection light separated into wavelengthsby the spectrometer 42.

The processor 50 computes the distance between the sensor head 30 andthe measurement object 2 on the basis of the detection values from eachlight receiving element among the plurality of light receiving elementsin the light receiving unit 40. A relational expression between a pixel,a wavelength, and a distance value can be preliminarily set, forinstance, by being permanently stored in the processor 50 when shippingthe device. Therefore, the processor 50 can compute the displacementusing the received light waveform (i.e., pixel information) output fromthe light receiving unit 40.

FIG. 3 illustrates an example of a sensor head cable with a plurality ofcables connected in series; this arrangement is for improving usability.That is, the sensor head cable in this example contains three cables241, 243, 245. A connector 242 is inserted between the cable 241 and thecable 243 to optically connect the cables, and another connector 244 isinserted between the cable 243 and the cable 245 to optically connectthe cables.

The light guide 20 contains a combiner/divider (coupler) 23 foroptically coupling the input cable 21 and output cable 22 with thesensor head cable. The functions of the combiner/divider 23 were alreadydescribed with reference to FIG. 2 , and thus a description therefor isnot repeated here.

With a combiner/divider serving as the coupler in the opticalmeasurement device 1 according to the embodiment, it is thereby possibleto split the light within the light guide 20, and allow a singledetector 44 to receive the light reflecting from the measurement object2 (measurement light) and propagating through the plurality of cores.

C. Problems with the Reflection Light

In principle, only the wavelength component in focus at the position ofthe surface of the measurement object 2 is reflected therefrom andenters the light receiving unit 40. Despite that, a portion of theillumination light may reflect partway through the light receiving unit40 (i.e., along the optical path of the illumination light from thelight source 10 to the sensor head); that reflection light may thenenter the light receiving unit 40.

FIG. 4 is a schematic view for explaining the reflection of a portion ofthe illumination light partway through the light guide 20. Asillustrated in FIG. 4 , this reflection of a portion of illuminationlight may occur, for instance in the combiner/divider 23 (coupler 231,232), connector 242, connector 244, or the connecting part between thesensor head 30 and the cable 245. Increasing or decreasing the power ofthe light source 10 can also bring about abnormalities in the returninglight.

A portion of the illumination light may reflect and return to the sensorhead when, for instance, the combiner/divider 23 is defective, or theconnector 242, 244 is damaged or dirty. The illumination light ispossibly scattered inside the optical fiber when a longer optical fiberis included in the cable. Moreover, a portion of the illumination lightmay be reflected by damage or dirt on the end surface of the fiber.

FIG. 5 is a schematic view for explaining the problems that arise when aportion of the illumination light is reflected partway through the lightguide 20. Referring to FIG. 5 , the processor 50 identifies the peakposition of the (radiant) intensity of the received light on the basisof the received light waveform (i.e., the radiant intensity profile ofthe received light). The processor 50 identifies a main componentwavelength among the wavelengths included in the reflection light fromthe wavelength corresponding to said peak position; the processor 50then computes the distance from the sensor head to the measurementobject 2 (i.e. the displacement) on the basis of the main componentwavelength identified (e.g., the wavelength λ2).

When the optical measurement device 1 is operating normally, the amountof noise component (i.e., the background noise) detected is sufficientlysmall. However, when a portion of the illumination light reflects in andreenters the light guide 20, the (radiant) intensity of the receivedlight increases in the noise components, i.e., in the wavelengths otherthan wavelength λ2.

FIGS. 6A and 6B are for describing how received signals are processedwithin an optical measurement device 1 according to the embodiment. FIG.6A is a waveform diagram for describing the received light waveformobtained when the optical measurement device 1 is operating normally.FIG. 6B is a waveform diagram for describing the received light waveformobtained when the optical measurement device 1 is operating abnormally.

As illustrated in FIG. 6A and in FIG. 6B, the optical measurement device1 according to the embodiment identifies the main component wavelengthon the basis of the received light waveform and a waveform generated bysubtracting a returning light waveform (i.e. obtaining the measurementwaveform). For instance, the returning light waveform can be obtainedbefore measuring the displacement, and stored internally in the opticalmeasurement device 1.

During normal operation of the optical measurement device 1, there is asmall difference between the returning light component contained in thereceived light waveform and the returning light within the waveformacquired in advance. The measurement waveform essentially cancels outthe returning light component, and thus the signal-to-noise ratio ishigh. Therefore, it is possible to very accurately identify the maincomponent wavelength.

Whereas, as illustrated in FIG. 6B, when there is a large returninglight component in the received light waveform, the returning lightcomponent within the received light waveform is not canceled out even ifthere is a difference between the received light waveform and thepreliminarily stored returning light component waveform. Therefore, thesignal-to-noise ratio of the measurement waveform is low. The lowersignal-to-noise ratio reduces the accuracy of detecting the peakwavelength, and therefore reduces the accuracy of measuring thedisplacement.

In the embodiment, the processor 50 monitors the received lightintensity of a specific wavelength. The processor 50 detects a receivedlight waveform as abnormal when the change between the received lightintensity in the specific wavelength is greater than or equal to athreshold in relation to the received light intensity when the opticalmeasurement device is operating normally. Moreover, the processor 50provides notification of the abnormality. The user may then, forinstance, clean the connectors 242, 244 or exchange the light guide 20to thereby remove the cause of the abnormal waveform. Additionally, ifthe amount of returning light increases because of lengthening theoptical fiber for instance, the value of the returning light componentmay be re-acquired and stored internally in the optical measurementdevice 1 to thereby remove the cause of the abnormal waveform.Accordingly, this allows the optical measurement device to continue toperform highly accurate displacement measurements. Embodiments of theinvention are described below in detail.

D. First Embodiment

FIG. 7 is a schematic waveform diagram for explaining how, according tothe first embodiment, the optical measurement device 1 assessesabnormalities. Referring to FIG. 3 and FIG. 7 , the light receiving unit40 measures the received light intensity I1, I2, I3, I4, I5 in thewavelengths λ1, λ2, λ3, λ4, λ5 respectively. The processor 50 comparesthe received light intensity in each of the wavelengths with a referencevalue for the wavelength (i.e., the received light intensity duringnormal operation). For instance, the reference value may be setinitially when shipping the product. When swapping a sensor head in orout on site, the user may press an operation button (not shown) on theoptical measurement device 1 to reset the reference values.

The processor 50 determines, for each of the wavelengths whether or notthe difference between the received light intensity and the referencevalue exceeds a threshold. If the difference between the received lightintensity and the reference value exceeds the threshold for all thewavelengths λ1, λ2, λ3, λ4, λ5, the processor 50 determines there is anabnormality in the optical measurement device 1. The reference value andthe threshold may be set for each wavelength and stored internally inthe processor 50.

More wavelengths may be used for comparing the received light intensityand the reference value than the number of surfaces on the measurementobject 2 for which the displacement is measured. The optical measurementdevice 1 may detect a plurality of surfaces; this may occurs when themeasurement object 2 is transparent. When the measurement object 2 istransparent, the peaks appear in received light waveform; the number ofpeaks corresponds to the number of wavelengths, which corresponds to thenumber of front surfaces and rear surfaces on the transparentmeasurement object 2. The number of thresholds is determined inaccordance with the peaks in the received light waveform. Displacementis measured is for at least one surface. Hereby it is possible to detectan abnormal waveform on the basis of the received light intensity inanother wavelength even if one of the wavelengths selected from theplurality of wavelengths coincides with the measurement wavelength.

Next, the reason for using five wavelengths in the first embodiment isgiven below. FIG. 8 is a diagram for explaining how the opticalmeasurement device 1 according to the embodiment measures thedisplacements of a plurality of surfaces on the measurement object 2.

As illustrated in FIG. 8 , the measurement object 2 is, for instance,made up of two transparent bodies (e.g. glass) with a spacer interposedto create a space therebetween. The measurement object 2 contains foursurfaces 2A, 2 b, 2 c, 2 d with different displacements; these foursurfaces are the two front surfaces (2 a, 2 b) of the transparent bodiesand the two rear surfaces (2 c, 2 d) of the transparent bodies.Therefore, the optical measurement device 1 measures the displacementsof the two front surfaces and the two rear surfaces of the transparentbodies. The wavelength used to detect an abnormal waveform may beselected as desired. However, although all four wavelengths may beselected to detect the abnormal waveform, it is necessary to considerthe possibility that the four wavelengths selected will coincide with awavelength whose focal point is at the two front surfaces or the tworear surfaces of the measurement object 2 (i.e., the two transparentbodies). It is therefore necessary to ensure the number of wavelengthsdiffers from the number of surfaces to be detected.

In the example illustrated in FIG. 8 , the focal position for thewavelength component λ5 in the illumination light differs from thepositions of the surfaces 2 a, 2 b, 2 c, 2 d. Therefore, the opticalmeasurement device 1 can detect an abnormality by comparing thewavelength component λ5 in the received light waveform and the referencevalue.

A user may use machine learning results to set the wavelengths andthresholds. The wavelengths and thresholds may be established inaccordance with the spectrum emitted by the light source 10. Note thatthe wavelengths and thresholds may be set in advance, for instance, whenshipping the optical measurement device.

FIG. 9 schematically illustrates changes in the received light intensityof background components when a portion of the illumination lightreflects partway through the light guide 20. Referring to FIG. 9 , whena portion of the illumination light is reflected partway in the lightguide 20, the amount of change in the returning light components dependson the wavelength. For instance, the threshold for a wavelength close tothe peak of the returning light component is relatively greater thanother thresholds because the amount of change in the returning lightcomponent tends to be larger. In contrast, for wavelengths shorter orlonger than the peak wavelength in the returning light component, thethreshold is relatively smaller than the other thresholds because theamount of change in the returning light component tends to be smaller.It is hereby possible to perform more precise detection of an abnormalwave form.

FIG. 10 illustrates an example of the relationship between a monitoredwavelength and a threshold. As depicted in FIG. 10 , n thresholds Th1,Th2, . . . , Thn are established for n wavelengths λ1, λ2, . . . , λn,where n is an integer greater than or equal to 2. In FIG. 8 , n=5;further, the relationship depicted in FIG. 10 is stored in the processor50.

FIG. 11 is a flowchart for explaining the process of detecting anabnormal waveform according to the first embodiment. Referring to FIG. 3and FIG. 11 , once processing starts, in step S1 the processor 50compares the received light intensity (i.e., the wavelength component)for each of the wavelengths λ1, λ2, . . . , λn with the reference value.In step S2, the processor 50 determines whether or not the amount ofchange in the received light intensity is greater than or equal to thethreshold for all the wavelengths.

If the amount of change in the received light intensity in relation tothe reference value is greater than or equal to the threshold in all thewavelengths (YES, at step S2), in step S3, the processor 50 detectsthere is an abnormal waveform. In this case, in step S4 the processor 50alerts the user that an abnormal waveform was detected. The method ofnotification is not particularly limited, and may be as sound or lightvia a known method.

Whereas, if the amount of change in the received light intensity inrelation to the reference value is less than the threshold for at leastone wavelength (NO, at step S2), in step S5, the processor 50 measuresthe displacement on the basis of the received light waveform. After themeasurement of the displacement is complete, the flow returns to stepS1.

E. Second Embodiment

In a second embodiment, the optical measurement device 1 detects anabnormal waveform on the basis of the amount of change in the receivedlight intensity for a single wavelength. This optical measurement device1 is configured identically to the first embodiment; therefore, thedescription of the configuration is not repeated.

FIG. 12 is a diagram for describing the spectrum emitted by the lightsource 10 to explain the process of detecting an abnormal waveformaccording to the second embodiment. Referring to FIG. 12 , a wavelengthdomain 60 is the wavelength domain used for measuring the displacementand is referred to as the “measurement range”. To detect abnormalwaveform in the second embodiment, a single wavelength is selected froma wavelength domain 61 or a wavelength domain 62, which are outside themeasurement range. As with the first embodiment, a waveform is detectedas an abnormal waveform when the amount of change in the received lightintensity (wavelength component) within the selected wavelength isgreater than or equal to a threshold. Consequently, the effects onmeasuring the displacement of the object can be reduced because thereceived light intensity is monitored in a single wavelength selectedfrom a wavelength domain outside the measurement range.

FIG. 13 is a flowchart for explaining the process of detecting anabnormal waveform according to the second embodiment. Referring to FIG.11 and FIG. 13 , that is S11 and S12 are executed in place of steps S1and S2 in the second embodiment. In step S11 processor 50 compares thereceived light intensity of a wavelength λ_(o) outside the wavelengthdomain 60 to the reference value. The wavelength λ_(o) is established inadvance. In step S12, the processor 50 determines whether or not theamount of change in the received light intensity is greater than orequal to the threshold for the wavelength λ_(o).

If the amount of change in the received light intensity in relation tothe reference value is greater than or equal to the threshold (YES, atstep S12), the processor 50 continues to step S3 and detects that thereis an abnormal waveform. In step S4, the processor 50 alerts the userthat an abnormal waveform was detected. In contrast, if the amount ofchange in the received light intensity in relation to the referencevalue is less than the threshold (NO, at step S12), the processor 50continues to step S5. Here, the processor 50 measures the displacement.After measurement of the displacement is complete, the flow returns tostep S11.

Note that in the second embodiment, determining whether or not thereceived light waveform is abnormal is carried out based on the amountof change in a wavelength outside the measurement range. Therefore, aplurality of wavelengths may be selected from within a wavelength domainoutside the measurement range, and the detection of an abnormal waveformcarried out on the basis of the amount of change in the received lightintensity in the plurality of wavelengths.

F. Advantages

As above described, an optical measurement device 1 according to theembodiments detects whether a received light waveform is abnormal.Moreover, the optical measurement device according to the embodimentsensures a user is made aware that the received light waveform isabnormal. When an increase in the returning light reduces themeasurement accuracy, the device detects the abnormality in the receivedlight waveform. A user may take appropriate action to improve thereduced accuracy upon notification from the optical measurement device1, e.g., cleaning a connector; and, if there is an increase in thereturning light because of lengthening the optical fiber, the user mayre-acquire the value for the returning light component, and store thevalue in the processor. Therefore, it is possible to re-establish highlyaccurate measurement even when the accuracy of measuring thedisplacement had deteriorated.

All aspects of the embodiments disclosed should be considered merelyexamples and not limitations as such. The scope of the present inventionis not limited to the above description but to the description in theclaims, and is intended to include all equivalents and modificationsallowable by the claims.

What is claimed is:
 1. An optical measurement device comprising: a lightsource configured to emit illumination light including a plurality ofwavelength components; a sensor head configured to introduce an axialchromatic aberration into the illumination light from the light sourceand to receive reflection light reflecting from a measurement objectwhere at least a portion of the measurement object lies along a lineextending from the optical axis of the sensor head; a light receivingunit; a light guide configured to guide light between the light sourceand the sensor head and between the sensor head and the light receivingunit, the light receiving unit configured to receive the reflectionlight received at the sensor head or returning light generated by areflection of a portion of the illumination light partway through thelight guide, and to separate the reflection light or the returning lightinto wavelength components and thereby receive light having thewavelength components; and a processor configured to compute thedistance from the sensor head to the measurement object on the basis ofa received light intensity of the wavelength components received in thelight receiving unit; the processor compares a received light intensityof a wavelength component to a reference value for the wavelengthcomponent for a plurality of wavelength components in a waveformrepresenting the light received, and determines, on the basis of theresult of comparison, whether or not to allow a measurement of thedistance to the measurement object, the processor does not allow themeasurement of the distance to the measurement object when the processordetects an abnormality in an amount of the received light, the processordetects the abnormality when a difference between the received lightintensity and the reference value therefor is greater than or equal to apredetermined threshold for all wavelength components in the pluralityof wavelength components, and the processor measures the displacement ofthe measurement object when the difference between the received lightintensity and the reference value therefore is less than thepredetermined threshold for at least one wavelength component in theplurality of wavelength components.
 2. The optical measurement deviceaccording to claim 1, wherein the processor measures the displacement ofthe measurement object on the basis of a peak wavelength in the receivedlight waveform when the amount of change in the received light intensityis less than a threshold for at least one of the plurality of wavelengthcomponents.
 3. The optical measurement device according to claim 1,wherein the plurality of wavelength components include five wavelengths.4. The optical measurement device according to claim 1, wherein saidthreshold is defined for each wavelength on the basis of the spectrumemitted by the light source.
 5. An optical measurement devicecomprising: a light source configured to emit illumination lightincluding a plurality of wavelength components; a sensor head configuredto introduce an axial chromatic aberration into the illumination lightfrom the light source and to receive reflection light reflecting from ameasurement object where at least a portion of the measurement objectlies along a line extending from the optical axis of the sensor head; alight receiving unit; a light guide configured to guide light betweenthe light source and the sensor head and between the sensor head and thelight receiving unit, the light receiving unit configured to receive thereflection light received at the sensor head or returning lightgenerated by a reflection of a portion of the illumination light partwaythrough the light guide, and to separate the reflection light or thereturning light into wavelength components and thereby receive lighthaving the wavelength components; and a processor configured to computethe distance from the sensor head to the measurement object on the basisof a received light intensity of the wavelength components within afirst wavelength domain received in the light receiving unit, the firstwavelength domain being equivalent to a predetermined measurement rangeused to measure a displacement of the measurement object; the processorcompares a reference value for a received light intensity and thereceived light intensity of a wavelength component within a secondwavelength domain outside the first wavelength domain to detect anabnormality in an amount of the received light when the differencebetween the received light intensity and the reference value is greaterthan or equal to a predetermined threshold for the wavelength componentin the second wavelength domain.
 6. The optical measurement deviceaccording to claim 5, wherein, the processor provides notification ofthe abnormality when the abnormality is detected.
 7. An opticalmeasurement device comprising: a light source configured to emitillumination light including a plurality of wavelength components; asensor head configured to introduce an axial chromatic aberration intothe illumination light from the light source and to receive reflectionlight reflecting from a measurement object where at least a portion ofthe measurement object lies along a line extending from the optical axisof the sensor head; a light receiving unit; a light guide configured toguide light between the light source and the sensor head and between thesensor head and the light receiving unit, the light receiving unitconfigured to receive the reflection light received at the sensor heador returning light generated by a reflection of a portion of theillumination light partway through the light guide, and to separate thereflection light or the returning light into wavelength components andthereby receive light having the wavelength components; and a processorconfigured to compute the distance from the sensor head to themeasurement object on the basis of a received light intensity of thewavelength components received in the light receiving unit; theprocessor compares a received light intensity of a wavelength componentto a reference value for the wavelength component for a plurality ofwavelength components in a waveform representing the light received anddetermines, on the basis of the result of comparison, whether or not toallow a measurement of the distance to the measurement object, and theprocessor measures the displacement of the measurement object when thedifference between the received light intensity and the reference valuetherefor is less than the predetermined threshold for at least onewavelength component in the plurality of wavelength components, when theresult of comparison is normal; whereas the processor does not allow themeasurement of the distance to the measurement object when the processordetects an abnormality in an amount of the received light, the processordetects the abnormality when the difference between the received lightintensity and the reference value therefor is greater than or equal to apredetermined threshold for each wavelength component in the pluralityof wavelength components, and the processor provides notification of anabnormality.
 8. An optical measurement device comprising: a light sourceconfigured to emit illumination light including a plurality ofwavelength components; a sensor head configured to introduce an axialchromatic aberration into the illumination light from the light sourceand to receive reflection light reflecting from a measurement objectwhere at least a portion of the measurement object lies along a lineextending from the optical axis of the sensor head; a light receivingunit; a light guide configured to guide light between the light sourceand the sensor head and between the sensor head and the light receivingunit, the light receiving unit configured to receive the reflectionlight received at the sensor head or returning light generated by areflection of a portion of the illumination light partway through thelight guide, and to separate the reflection light or the returning lightinto wavelength components and thereby receive light having thewavelength components; and a processor configured to compute thedistance from the sensor head to the measurement object on the basis ofa received light intensity of the wavelength components within a firstwavelength domain received in the light receiving unit, the firstwavelength domain being equivalent to a predetermined measurement rangeused to measure the displacement of the measurement object; theprocessor compares a reference value for a received light intensity andthe received light intensity of a wavelength component within a secondwavelength domain outside the first wavelength domain, and the processorprovides notification of an abnormality in an amount of the receivedlight when the processor detects the abnormality when the differencebetween the received light intensity and the reference value is greaterthan or equal to a predetermined threshold for the wavelength componentin the second wavelength domain.
 9. The optical measurement deviceaccording to claim 7, wherein the light guide includes: a cable coupledto the sensor head and coupled to the light source and the lightreceiving unit, and the abnormality is an abnormality relating toreflection of a portion of the illumination light at a connecting partbetween the sensor head and the cable.
 10. The optical measurementdevice according to claim 7, wherein the light guide includes: a cablecoupled to the sensor head and coupled to the light source and the lightreceiving unit; and a combiner provided on the cable, and theabnormality is an abnormality relating to reflection of a portion of theillumination light due to defectiveness of the combiner.
 11. The opticalmeasurement device according to claim 7, wherein the light guideincludes: a cable coupled to the sensor head and coupled to the lightsource and the light receiving unit; and a divider provided on thecable, and the abnormality is an abnormality relating to reflection of aportion of the illumination light due to defectiveness of the divider.12. The optical measurement device according to claim 7, wherein thelight guide includes: a plurality of cables; and at least one connectorfor connecting the plurality of cables in series, and the abnormality isan abnormality relating to reflection of a portion of the illuminationlight due to defectiveness of the at least one connector.
 13. Theoptical measurement device according to claim 7, wherein the light guideincludes: a plurality of cables; and at least one connector forconnecting the plurality of cables in series, and the abnormality is anabnormality relating to scattering of a portion of the illuminationlight due to the length of the plurality of cables connected in series.14. The optical measurement device according to claim 7, wherein thelight guide includes a cable including an optical fiber, and theabnormality is an abnormality relating to reflection of a portion of theillumination light due to damage on an end surface of the optical fiber.15. The optical measurement device according to claim 7, wherein thelight guide includes a cable including an optical fiber, and theabnormality is an abnormality relating to reflection of a portion of theillumination light due to dirt on an end surface of the optical fiber.